1. Field of the Invention
The present invention relates to image scanning apparatus having a scanning station mounted on a scanning station sub-frame which scanning station comprises means for transporting a recording medium and scanning means for scanning the thus-transported recording medium with a beam of radiation, there being also provided a separate sub-frame carrying additional means for transporting the recording medium towards and away from the scanning station.
Such scanning apparatus may take any of various specific forms depending on the specific nature of the purpose which it is to serve. The apparatus may be designed so that an image (whether latent or visible) is formed on the recording medium during such scanning, or it may be designed so that a pre-existing image carried by the recording medium is read during scanning so that it may be transferred to some other medium. Purely by way of example, in the photo-copying field, the scanning beam could be a beam of visible light and the radiation collecting means could be arranged to collect light reflected from a visible image borne by the recording medium. Alternatively, the beam could be a thin pencil of laser radiation which scans the recording medium transversely of its direction of transport through the scanning station. In such cases, the radiation collecting means could be arranged to collect light reflected from a visible image of the recording medium, or, given a suitable recording medium, the radiation collecting means could be arranged to collect light emitted from a latent image carried by the recording medium in response to the incidence of the laser beam. Such recording media are used in photo-stimulable luminescence ("PSL") radiography.
In the PSL radiographic system, a PSL. X-ray plate has applied thereto a layer of a photostimulable luminescent material which comprises a phosphor, for example a europium-activated barium fluorohalide, and a binder. The phosphor has the characteristic of being energised to an excited state by X-rays, and can then be stimulated by visible or infra-red light to return to the ground state with the emission of visible light (of a different wavelength from the stimulating light). The excited state has a half-life of at least several hours or days in the absence of stimulating light. A PSL plate is potentially re-usable many times. The technique is described in an article by Sonoda et al. in Radiology, Volume 148 (September 1983), at pages 833 to 838, and it offers the potential advantages of better image resolution at lower X-ray dosages for the patient.
The present invention was made with specific reference to the scanning of PSL radiographic plates, but the underlying principle may also be applied to other image scanning systems, for example in the fields of photocopying and the digital encoding of images for computer storage or manipulation or for transmission by wire or wireless means.
A major problem confronting the user of image scanning apparatus is the transmission of vibrations to the recording medium during actual scanning thereof. The problem is perhaps at its most severe in the case of continuous feed apparatus where a succession of discrete pieces of recording medium are being fed through the apparatus, and where several operations are required to be performed in the apparatus. For example, one could envisage an integrated apparatus for digitally encoding the information carried by a conventional X-ray plate which comprised means for removing an exposed photographic plate from a cassette and for developing and fixing the photographic image, for drying and then scanning the plate, and for ejecting the scanned plate and the used cassette, possibly reloaded with a fresh X-ray plate, all with associated transport mechanisms. It will readily be appreciated that all this mechanical activity could give rise to quite considerable vibration in the apparatus and that this could adversely affect the scanning resolution and reliability.